00 BOTANICAL MICROTECHNIQUE. 



blackened by osmic acid and deeply stained by alcannin or 

 cyanin (cf. 109-1 1 1). 



Most ethereal oils are also readily soluble in glacial acetic 

 acid and in an aqueous solution of c/iloral hydrate. 



[Mesnard (I) has used the following method for distin- 

 guishing the ethereal from the fatty oils. He cemented two 

 glass rings of different sizes concentrically to a slide, the 

 inner ring being also lower than the outer. The space be- 

 tween the two rings was filled with strong hydrochloric acid, 

 and the sections to be examined were placed on the under 

 surface of a cover-glass resting on the outer ring, in a hang- 

 ing drop of glycerine containing a large proportion of sugar. 

 Other sections may be placed, for longer exposure, on a 

 small cover that rests on the inner ring. In this apparatus 

 the HC1 is taken up with water by the glycerine, and, after 

 a time, the ethereal oils present exude in golden-yellow 

 drops, which later disappear. This exudation in drops never 

 occurs with fatty oils.] 



It may be observed here that J. Behrens (I) has seen on 

 the glandular hairs of Ononis spinosa a strongly refractive 

 secretion which became colored deep red, even in very 

 dilute aqueous solutions of fuchsin. Nothing definite can 

 be said as to the chemical composition of this secretion, but 

 it is probable that it belongs in the category of ethereal 

 oils. 



b. Resins and Terpenes. 



145. The Unverdorben-Franchimont reaction with copper 

 acetate may be used as a special reagent for resins and ter- 

 penes. Large pieces of the parts of plants to be examined 

 may be placed in a concentrated aqueous solution of the salt 

 named, and studied after not less than about six days. The 

 resins then appear colored a beautiful emerald-green. The 

 copper acetate may be removed before cutting by washing 

 with running water. Pieces so treated may be preserved in 

 50$ alcohol ; and microscopic preparations retain their beau- 

 tiful color in glycerine-gelatine. 



